This invention generally relates to a shock absorbing structure for absorbing shock in a vehicle. More particularly, the present invention pertains to a shock absorbing member and a bumper for a vehicle which absorbs impact energy through plastic deformation to absorb the axial compressive load.
In general, vehicles are provided with a shock absorbing member for absorbing the impact energy arising upon a collision or other type of impact. A collision causes an axial compressive load and this load is applied to the shock absorbing member. The shock absorbing member absorbs the impact by repeating a bellows-like buckling deformation continuously. Ideally the shock absorbing member should advance the stable buckling deformation when the axial compressive load is applied. That is, as shown in FIG. 7, in order for the shock absorbing member to advance the buckling deformation during application of the axial compressive load, the shock absorbing member should ideally have a rectangular wave shaped characteristic in which the corresponding axial compressive load is a generally constant value with respect to the stroke or the amount of deformation.
One type of material having such a superior rectangular wave shaped characteristic is aluminum alloy material formed by extrusion. Examples of shock absorbing members adopting this aluminum alloy material are disclosed in Japanese Patent Laid-Open Publication No. 6(1994)-247338, Japanese Patent Laid-Open Publication No. 8(1996)-268323, Japanese Patent Laid-Open Publication No. 8(1996)-310440, Japanese Patent Laid-Open Publication No. 11(1999)-29064, Japanese Patent Laid-Open Publication No. 11(1999)-208519, and Japanese Utility Model Laid-Open Publication No. 7(1995)-35252.
From the point of view of the adoption to a vehicle, however, these shock absorbing members having a rectangular wave shaped characteristic do not always show good characteristics and performance. That is, when this shock absorbing member is adopted to a vehicle, as shown in FIG. 7, the proof stress FB of a vehicular body is set so as to be somewhat larger than the above mentioned roughly constant value of the axial compressive load. Then, when the buckling deformation of the shock absorbing member is advanced within the range of the proof stress FB of the body, the impact energy at the collision is absorbed. In recent years, however, the safety performance during high speed collision is has been of concern and the safety performance in the ODB (offset deformable barrier) collision which simulates an offset collision between vehicles is estimated. In this estimation, even if the proof stress of the body of one vehicle (own vehicle) is large and the one vehicle could decelerate and absorb the impact energy while destroying only another vehicle (the other vehicle), a good result is not obtained. Ideally, it is desirable that both vehicles be destroyed just the same (or that neither vehicle be destroyed significantly more than the other) and that both vehicles are able to decelerate while absorbing the impact energy. In other words, it is necessary to consider not only the safety performance of one vehicle but also the assailing performance to another vehicle.
The axial compressive load accompanying the collision and applied to the shock absorbing member is transmitted to the body and also to another vehicle as a reaction force. Accordingly, the axial compressive load against the shock absorbing member becomes a criteria for the assailing performance to another vehicle. That is, it is necessary that the axial compressive load to the shock absorbing member which is transmitted to another vehicle as the reaction force is set smaller than the proof stress of the body of the other vehicle.
In situations where the above mentioned shock absorbing member is adopted, however, the axial compressive load to the shock absorbing member which is transmitted to another vehicle as the reaction force is a roughly constant value. Accordingly, it is necessary that the axial compressive load characteristic of the shock absorbing member be set while fixing the proof stress of the body of another vehicle as a standard regardless of the proof stress of the body of the one vehicle. As a result, the absorption of the impact energy becomes insufficient. Further, if the length of the shock absorbing member increases for absorbing sufficient impact energy by increasing the stroke (i.e., the amount of deformation), it is necessary to provide a large space for disposing the shock absorbing member.
Accordingly, a need exists for an improved shock absorbing member and a bumper which is not as susceptible to the drawbacks identified above.
According to one aspect of the present invention, a shock absorbing member for a vehicle which absorbs the impact energy in a plastic deformation manner so that the axial compressive load is absorbed has a hollow structure whose cross-section is constant and whose axis is adapted to extend forward and rearward of the vehicle. The shock absorbing member is constructed so that the axial compressive load is gradually increased according to advance of the plastic deformation.
When the plastic deformation advances, the corresponding axial compressive load is increased gradually. Accordingly, the axial compressive load applied upon the occurrence of a collision increases gradually to accompany the advance of the plastic deformation. For example, when one vehicle collides against another vehicle, the axial compressive load which increases gradually according to the advance of the plastic deformation is transmitted to another vehicle as a reaction force. Because the axial compressive load in the initial stage of the plastic deformation is low, the assailing performance to the other vehicle is decreased. Further, because the axial compressive load increases gradually within the range of the proof stress FB of one vehicle according to the advance of the plastic deformation, sufficient impact energy is absorbed.
According to another aspect of the invention, a shock absorbing member for a vehicle which absorbs the impact energy in a plastic deformation manner with the axial compressive load being absorbed includes a hollow member whose cross-section is constant and whose axis is adapted to extend forward and rearward of the vehicle and a flange which is formed on the hollow member roughly along the axis of the hollow member. The projecting amount of the flange increases gradually from one side toward the other side of the hollow member.
In accordance with another aspect of the present invention, a vehicle bumper includes a bumper reinforcing member, a body, and a pair of hollow crash boxes each of which extends forward and rearward of the vehicle and each of which has a roughly constant cross section. Each crash box has one end fixed to the bumper reinforcing member and the other end fixed to the body. Each crash box also has a flange whose projecting amount increases gradually from one side toward the other side of along the axis of the crash box.
The foregoing and additional features and characteristics of the present invention will become more apparent from the following detailed description considered with reference to the accompanying drawing figures in which like reference numerals designate like elements.
FIG. 1 is a perspective view of a crash box according to one embodiment of the present invention.
FIG. 2 is a perspective view of a front portion of a vehicle to which is applied the crash box of the present invention as shown in FIG. 1.
FIG. 3 is a graph showing the relationship between the axial compressive load and the stroke associated with the present invention.
FIG. 4 is a perspective view of a modified version of the crash box.
FIG. 5 is a perspective view of another modified version of the crash box.
FIG. 6 is a perspective view of a further modified version of the crash box.
FIG. 7 is a graph showing the relationship between the axial compressive load and the stroke of a known shock absorbing member.